Harry thomas mabstoet



H. T. lMARSTON.

PARALLEL RULER ron- LAcKoARDs AND THE LIKE.

APPLICATION FILED APR. 4. |918.

l ,323,051 u Patented Nov. 25, 1919.

K #TAM/752227; f

para eraan rara HARRY THOMAS Mener-on, or ianre'rrnnncnrn or GOOD HOPE, SOUTH AFRICA.

PARALLEL-RULE?. FOR BLACKBOARDS AND THE LIKE.

specification of Letters Patent.

'Application filed April 4, 1918. Serial 170.226,720.

To all wwm 1t/may concern Be it known that l, HARRY THOMAs Mans- 'ro1-.', a subject of the King of England, residing at Matatiele, in the Province of the Cape of Good Hope and Union of South Africa, have invented a new and useful Parallel- Ruler for Blackboards and the like.

The present invention consists in an arrangement for guiding ruler for movement parallel with itself over a blackboard or the like, which permits the ruler to he readily moved and causes it to remain where placed on a. vertical or other board.

ln the drawings Figure 10 shows a blackboard fitted with the invent-ion. Y

Fig. 1 is an enlarged view of the left hand end of the ruler with the adjacent parts of the blackboard and its frame parts being broken away.

Fig. 2 is an end view of the ruler.

Fig. 3 is a view of Fig. 2 seen from the left.

Fig. v-l is a sectional plan, taken through the ruler. Y

Fig. 5 a sectional plan of the opposite end of the device taken 0n a. plane above the ruler.

Fig. G is section on A--A Fig. 10 with the ruler at the bottom of the board.

Fig. 7 is a fragmentary view of the right hand top corner of the board.

Fig. 8 is a plan of the same with the corner cover 21 removed.

Fig. 9 shows a straining pin hereafter referred to.

Fig. 10 indicates a blackboard or the like mounted in a frame 8, 12, 13, 15. The side members 8, 13 are rabbeted at 7 to form a guideway for the ruler 1` In a recess at the left hand end of the ruler is a double grooved roller 3 each element of which is of equal diameter. A similar roller 3a of the same diameter is provided at the right hand end of the ruler.

A stretched wire 6 is fixed at 9a at the right hand top corner of the frame, passes around beneath one element of the roller 3a, across the ruler, over one element of the other roller 3 and is secured vat 19a at the lower left hand side of the frame.

A similar wire 5 is symmetrically disposed, that is to say, it is xed at 9 at the left hand top corner of the frame, passes beneath the second element of the left hand roller 3, across the ruler, over the second element of the right hand roller 3 and is secured to the lower right hand corner 19 of the frame. The positions of points 9, 19, 9a and 19 and of the roller 3, 3a are such that between each of said points 9 and 19a, 9a, and 19 the wires are parallel to the direction of movement of the ruler 1.v

lt will be apparent that as the ruler is moved up or down, the length of wire fed from the perpendicular section of wire at each side is equal to the length fed into such perpendicular section, also the length of wire fed on and off is equal at each end of the ruler. The two ends of the ruler are therefore constrained to move equally and the ruler moves parallel with itself. Morcover the wires are strained taut and provide sufficient frictional resistance to cause the ruler to remain in any one position to which it is moved.

For effecting and maintaining the tautness of the wires the latter are secured at the top end to a revoluble straining pin 17 (F ig. 7 let into the frame. Access to this in is afforded by removing the corner cover plate 21. A recess 18 extending from the upper edge of the fra-me to the pin is provided for securing the wire through the pin.

20 is a linger recess formed in the lower edge of the ruler to facilitate raising the latter when it is at the bottom of the board.

11 are linger recesses for grasping the ruler.

14 is a channel in the lower frame mem` ber for holding chalk. Smooth-surfaced round pins may in some cases replace the rollers 3, 3a.

Having now particularly described and ascertained the nature of this invention and in what manner the same is to be performed I declare that what I claim is z- 1. A device of the character described including in combination, a blackboard, a frame surrounding the blackboard and provided with opposed longitudinal grooves onv the inner faces of the ends thereof, a ruler having a longitudinal recess 'in the rear face thereof and having its end portions slidably arranged in the grooves in the frame, rollers rotatably mounted in the recess at tie opposite ends of the ruler and means for constraining the ruler for movement parallel with the sides of the frame and composed of two fiexible members having their ends connected to opposite corners of the frame and having their medial portions trained respectively under the adjacent Patented Nov. 25,1919.

roller and over the remaining roller, and means #for adjusting tension of the said members.

2.' A device of the character described including in combination, a blackboard, a frame surrounding the blackboard and provided With opposed'longitudinal grooves on the inner faces of the ends thereol, and also provided on the sides and endsnear opposite corners with communicating passages, a ruler having a recess therein and having the ends slidably arranged Within grooves, rollers rotatably mounted in the recesses at the opposite ends thereof, means for con-l straining the ruler for movement parallel iframe parallel to the direction of movement of the ruler thence beneath the adjacent roller, thence overV the other roller and thence parallel to the direction of movement o1E the ruler to the diametric Voppositev corner of the frame, and tension pins mounted 1n certain of the passa-ges to which the outer ends of the members are connected. 7);-,

Dated this 30th day of November, 1917, at Matatiele, Cape of Good Hope, South Africa.

HARRY THUMAS MARSTON., 

